A data class in Python can be used to store configuration settings for an application or service. Default configuration values are assigned to fields on the data class. However, the user can overload those values by using a class method to load the configuration settings from a file.
The configuration data class shown below defines price and quantity fields with default values. The load_toml class method is used to read the configuration settings from a TOML file.
import tomllib
from dataclasses import dataclass
@dataclass
class Config:
"""Configuration dataclass."""
price: float = 12.89
quantity: int = 4
@classmethod
def load_toml(cls, file: str):
"""Load configuration settings from a TOML file."""
with open(file, "rb") as f:
conf = tomllib.load(f)
return cls(**conf)
Examples of using this data class are shown next. The first example creates a config object with default values. The second example loads the configuration from a TOML file.
conf = Config()
print(f"{conf.price=}")
print(f"{conf.quantity=}")
# This prints the following:
# conf.price=12.89
# conf.quantity=4
conf2 = Config.load_toml("conf.toml")
print(f"{conf2.price=}")
print(f"{conf2.quantity=}")
# This prints the following:
# conf2.price=5.99
# conf2.quantity=2
The contents of the TOML file used in the example is:
